ELEVATED CARBON-DIOXIDE AFFECTS THE PATTERNING OF SUBSIDIARY CELLS INTRADESCANTIA STOMATAL COMPLEXES

The influence of elevated CO2 concentration (670 ppm) on the structure , distribution, and patterning of stomata in Tradescantia leaves was s tudied by making comparisons with plants grown at ambient CO2. Extra s ubsidiary cells, beyond the normal complement of four per stoma, were associated with nearly half the stomatal complexes on leaves grown in elevated CO2. The extra cells shared characteristics, such as pigmenta tion and expansion, with the typical subsidiary cells, The position an d shape of the extra subsidiary cells in face view differed in the gre en and purple varieties of Tradescantia. Substomatal cavities of compl exes with extra subsidiary cells appeared larger than those found in c ontrol leaves, Stomatal frequency expressed on the basis of leaf area did not differ from the control. Stomatal frequency based on cell coun ts (stomatal index) was greater in leaves grown in CO,enriched air whe n all subsidiary cells were counted as part of the stomatal complex. T his difference was eliminated when subsidiary cells were included in t he count of epidermal cells, thereby evaluating the frequency of guard cell pairs, The extra subsidiary cells were, therefore, recruited fro m the epidermal cell population during development, Stomatal frequency in plants grown at elevated temperature (29 degrees C) was not signif icantly different from that of the control (24 degrees C). The linear aggregations of stomata were similar in plants grown in ambient and el evated CO2. Since enriched CO2 had no effect on the structure or patte rning of guard cells, but resulted in the formation of additional subs idiary cells, it is likely that separate and independent events patter n the two cell types. Plants grown at enriched CO2 levels had signific antly greater internode lengths, but leaf area and the time interval b etween the appearance of successive leaves were similar to that of con trol plants. Porometric measurements revealed that stomatal conductanc e of plants grown under elevated CO2 was lower than that of control le aves and those grown at elevated temperature, Tradescantia was capable of regulating stomatal conductance in response to elevated CO2 withou t changing the relative number of stomata present on the leaf.